It was released in South Korea on January 31, 2012, under FNC Music and distributed by Mnet Media.

Filled with slow-tempo rock ballads, the album illustrated the musical growth of the band.

[1] Lead vocalist Lee Hongki explained that the band chose rock ballads to coincide with the cold weather in South Korea at the time.

[2] FNC Media stated that Grown-Up "may be their best album yet", explaining that "fans will be able to experience how much they boys have matured musically".

The mini-album Grown-Up and the full music video for "Severely" were both released on January 31.

The music video starred Lee Hongki and a female trainee of FNC Media as his love interest.

[15] By February 9, 2012, ten days after its release, the album sold-out the 50,000 physical copies that were produced.